1. Field of Invention
The present invention relates to a voltage regulator. More particularly, the present invention relates to a voltage regulator capable of regulating an input voltage in real time so as to maintain an output voltage level.
2. Description of Related Art
A conventional voltage regulator provides generally a stable output voltage without considering the load effect. However, when the transient change of a load current happens, the output voltage drops if the voltage regulator cannot provide a sufficient driving current in real time. Particularly, when a larger current driving capability is required, for example, the voltage drop phenomenon of an LCD panel source driver is more severe.
FIG. 1 is a voltage regulator according to the conventional art. The voltage regulator 100 includes a voltage generator 110 and a voltage regulation unit 120. The voltage generator 110 uses the common node of a current source IREF and a resistor R13 to provide an input voltage INT to the negative input terminal of an operational amplifier 122. Due to the principle of virtual short circuit, the voltage at the common node of a resistor R11 and a resistor R12 is equal to the input voltage INT. At this time, an output voltage OUT is generated at the common node of the resistor R11 and a P-type transistor (PMOS transistor) P11. A capacitor CL functions as stabilizing the output voltage OUT of the voltage regulator 100, such that the output voltage OUT will not change severely along with the transient change of the load current 130. As shown in FIG. 1, the greater the load current IL changes, the more severe the output voltage OUT drops. Therefore, the voltage regulator 100 is required to effectively enhance the driving capability of the voltage regulation unit 120 when the output voltage OUT drops.